High power electrical resistors are known and used in many applications. For example, power resistors are used by heavy industry and electrical utilities as neutral grounding resistors; damping resistors; in harmonic filters; in speed controls; for motor starting; and the like.
Known power resistors may take the form of an edgewound conductor mounted on a insulating core. For example one such resistor is formed by winding a steel strip about the edge of a ceramic core. Alternatively, insulated wire conductor mounted about an insulating core forms a wire wrapped resistor.
Other power resistors take the form of a solid conductive ribbon, having a current path from end to end. The ribbon is bent in an accordion-like shape to reduce the size of the resistor while maintaining the relatively long current conducting path. Further known resistors are made of a plurality of stamped grids connected in series, or of a helical wire wrapped about a cylindrical core.
As is well known and understood, the resistance of a resistor is directly proportional to the effective length of the conductive element used to form the resistor. The resistance of the known power resistors is thus limited by the length of conductive material used to form the resistor.
One further known design incorporates a resistive slab having a plurality of circular holes or slots. These circular holes create a non-linear current path along the resistor, and provide for improved heat transfer and ventilation of the resistor. However, the choice of arrangements of circular holes does not provide for an optimum resistance.
It is an object of the present invention to provide an improved power resistor that overcomes some of the disadvantages of known devices.